[TYPO3-english] TYPO3 Fatal Error: problems with rights on typo3temp directory

[Sébastien L]

Here is the message I have when I try to access to typo3 (front or backend)

TYPO3 Fatal Error: The file was not written to the disk. Please, check that you have write permissions to the typo3temp/ directory.
The error on the administration interface is "
Oops, an error occured!

Lock file could not be created
"

The Typo3 Website  is on a PArallels Plesk server.
The only thing I've done is to restore a fully functionnal backuped version of my domain. So, I  have got no idea why I keep having this error. Thanks for the hel you could give to me.

Sébastien